Time for another update. This may be lengthy, so bear with me. I haven't had a lot of boat time lately, but I finally got it back out on the water on Friday. Here's what I had done leading up to Friday and what happened on the water.
I pulled the carbs again and this time soaked them for a good 4-5 hours in B-12. I blew out the passages and noticed one of the high speed orifice plugs was partially gummed up. I removed the plug and reamed it out. Every other passage was perfectly clear and unobstructed. I blew them out with more aerosol carb cleaner and compressed air and inspected again; still clean. The carbs were then reinstalled.
As I was paying a closer eye to timing and the butterfly plates after reinstalling and moving the throttle level, I noticed two things:
- First, the lower butterflies were not sitting perfectly horizontal like the upper butterflies. They were off just enough that I could see the brass plate looking dead center. I adjusted the lower carb linkage so that the lower butterflies were in sync perfectly with the upper butterflies; both at idle and at WOT.
- Second, there was some play in the throttle cable.I noticed that when I moved the fast lever to full, there was a lag between when I moved the lever and when the spark advance at the engine moved. I also noticed that when I moved the fast lever down (off), the spark advance at the engine would not only lag, but it wouldn't completely back down either. I disconnected the throttle cable at the engine and noticed that the black boot over the cable has some play in it. I would imagine this means I need to replace it, but for now I have to make do with it. To try and rectify the issue, I found a barrel screw where the cable is held up on the carb spacer plate thing. Trial-and-error, I turned the barrel screw to minimize the amount of lag and dead space at the spark advance. I also adjusted the travel stop screws as applicable.
Now, fast forward a couple of weeks and we're ready to hit the water. I put the boat on the muffs in the drive way to make sure I didn't really muck it up. The fast lever was 100% better, but still not perfect (I'll probably do a little more adjusting on it). The engine fired up as well as it always has (fast lever about 75%, hold the choke, crank). Idle seemed ok. I gave a very quick bump of throttle just to confirm and it seemed ok.
The main problem and reason for this thread has been my lean sneeze and subsequent engine die. The engine did not die out this time. The sneeze was barely noticeable, but still there. The only time I ever had the sneeze problem was at idle. With the fast lever up or while on the throttle, it had never presented itself. I suspect that I may have just put a bandaid over the problem and have not really cured it. My thinking is that in adjusting the throttle cable at the engine, I increased the idle RPM's enough to drown out the sneeze. Unfortunately, the tachometer does not work so I don't currently have a way of measuring RPM's other than by ear. I did not notice a discernible increase in RPM's since prior the adjustment, however.
With the basic checks ok, I headed to the lake. The engine fired up just the same. Took the same amount of time to warm up before I could get off the trailer. It hopped up on plane quickly and reached the exact same top speed that I am used to. Every appeared perfectly usual. At idle, the sneeze was still nearly gone. The only time the motor died out was after idling for more than a few minutes. It seemed that the longer I idled, the more frequent it began sneezing. Brief idle was perfectly fine. I was even able to power-load the boat back on the trailer, where it used to just bog down and die.
Back home, I pulled the plugs and gave everything an inspection. All 4 plugs looked exactly the same and no indication of fouling or lack of lubrication. I ran 18 gallons of gas over the entire day and ran the boat hard. No overheating or smoking. Nothing indicates to me that a cylinder is dropping or lean on lubrication. I would have expected a blown powerhead otherwise.
So what is next on a list of things to check? Perhaps a bad/weak coil? I haven't completely checked spark yet, but the plugs are brand new and gapped .30. I know my charging system is working (if that even has anything to do with it). The fuel pump is in excellent condition and no sediment. Bulb and fuel lines seem ok. Carbs are completely cleaned. Reed valves are in excellent shape. Compression is good.